When a truck, trailer or some other vehicle is parked at a loading dock, often some sort of vehicle restraint is used to keep the truck from inadvertently moving away from an elevated platform of the dock. This allows a forklift truck to safely drive between the dock platform and the truck for the purpose of loading or unloading the cargo inside the truck.
There are a variety of vehicle restraints available that can be installed at a loading dock for engaging the truck's RIG (Rear Impact Guard), also known as an ICC bar. An ICC bar is a beam that extends horizontally across the rear of a truck, just below the truck bed. Its primary purpose is to prevent an automobile from under-riding the truck in a rear-end collision. However, not all trucks have an ICC bar that can be readily engaged by an ICC-style restraint. Moreover, ICC bars are not prevalent outside the United States, so in those cases a wheel restraint can be used for blocking one or more of the truck's wheels.
Perhaps the most common wheel restraint is simply a wheel chock that wedges between the driveway and the underside of the wheel. However, wheel chocks often slip out of position on driveways that are slippery due to oil, rain, ice, sand, gravel or dirt. Moreover, wheel chocks usually are loose items that do not permanently attach to the loading dock area, so they often get misplaced.
One known example wheel restraint includes a wheel chock that is coupled to the loading dock by way of an articulated arm. To help prevent the chock from slipping out of its wheel-blocking position, the chock can be placed in mating engagement upon a serrated base plate that is anchored to the driveway. Although such a system can be effective, it does have some drawbacks.
First, a counterweight spring on the arm tends to prevent the wheel chock from resting its full weight upon the base plate. Second, the length to which the arm must extend to reach the wheel can adversely affect the angular relationship (about a vertical axis) between the mating surfaces of the chock and base plate. Third, although the known wheel restraint may include a sensor for detecting the presence of a wheel, the sensor does not indicate whether the chock is fully engaged with the serrations of the base plate. Finally, dirt, ice and other contaminants could hinder the engagement between the chock and the base plate, thus reducing the effectiveness of the chock.